The present invention relates to a new and improved construction of roller aprons or strand guide arrangement for a multiple strand billet- or bloom casting installation containing more than two strands for the continuous casting of metals, especially steel, wherein rollers or rolls of the at least partially curved roller aprons are driven individually by means of drive elements through the agency of power transmission shafts, the drive elements being arranged externally of the outer roller aprons.
The driving of driving rollers or the withdrawal and straightening rollers of a single-strand continuous casting installation is relatively simple to accomplish, since one or more motors are arranged adjacent the roller apron in an approximately coaxial position with respect to the rollers to be driven and are connected with such rollers by means of rigid or flexible shafts.
In the case of a twin-strand continuous casting installation the drive shafts of the related rolls of the second strand extend in the opposite direction, so that in this case the drive motors are located at the sides of both roller aprons which face away from one another. The spacing between the strands, which should be as small as possible for reasons well known in this technology (optimum utilization of the surface area, short tundish), is not in any way adversely affected.
In the case of multiple strand-continuous casting installations working with more than two strands for casting billets and blooms, the arrangement of the roller drives of the inner strands is, however, contradictory to the requirement for small spacing between the strands.
Owing to the smaller strand sectional shape or format for such installations and the therewith attendant smaller danger of bulging-out of the strand, the roller spacing is correspondingly great in the secondary cooling zone. The rollers, therefore, predominantly serve a guiding function. In the case of large strand sectional shapes or formats, for instance slabs, such rollers or rolls carry out as their primary function a supporting function and, therefore, there is selected a small roller spacing. The smaller strand shapes and the larger roller spacing in the case of billet- and bloom casting installations result in a significantly lower weight of the roller aprons or strand guide assembly in the secondary cooling zone. This lower weight does not require any subdivision of the roller aprons into selectively removable segments. The exchange of damaged parts of a roller apron is accomplished by withdrawing the entire roller apron or by time-consuming replacement of the damaged parts in the cooling compartment or chamber. However, with respect to space requirements and costs it is not possible to consider as economical the exchange of an entire roller apron.
Such installations are equipped with long dummy bars. If, however, there should be used short dummy bars, then there are required, apart from the drives for the withdrawal and straigtening unit also drives of some type for a limited number of rollers in the secondary cooling zone. The arrangement of electric motors with associated drives or gearing in the cooling chamber is complicated and owing to the hot, vapor-containing atmosphere which prevails therein there is impaired the operational reliability of the system. For the removal of a damaged roller apron such drives require, however, an initial dismantling and subsequent mounting thereof, resulting in longer downtimes of the entire continuous casting installation.
It is already known to arrange drive motors for the withdrawal and straigtening unit, in the case of multiple strand continuous casting installations, externally of the cooling chamber at the inside radius above the roller aprons, with articulated spindles extending downwardly at an inclination with respect to the rollers. However, this solution impairs the mounting or disassembly of the roller apron elements of the roller apron arranged therebelow. Also there must be employed stationary control panels or consoles for the motors, resulting in additional constructional expenditure.
It is also known in the art to extend at a withdrawal and straightening machine a roller over the width of the total number of strands and to drive such by means of a motor. However, such type common drive or driving roller for all of the strands requires an undesired drive coupling, which, for instance in the case of metal break-out at one of the strands, requires stoppage of the entire continuous casting installation. It is impossible to cast with non-controllable tundish-pouring outlets.
Furthermore, it is known in the case of three-strand and four-strand continuous casting installations to drive two rollers by means of independent motors, these rollers belonging to different roller aprons and being disposed transverse to the casting direction in alignment adjacent one another. Both of the motors are arranged at the same side externally of the outer roller aprons. The power transmission shaft for the drive rollers of the inner roller apron extends through the central bore of the drive rollers of the outer roller aprons. That this construction is complicated should be self-evident. For practical reasons, in this manner only rollers of two neighboring roller aprons can be driven, so that there can be constructed installations containing a maximum of four strands with a mirror-image arrangement of the motors. A great disadvantage furthermore resides in the fact that the dismantling of a driven roller of the outer roller apron simultaneously requires the dismantling of the corresponding drive rollers of the inner strand.